1. Field of the Invention
This invention relates to an apparatus for feeding sheets which have been cut sequentially from a long web.
2. Description of the Prior Art
In general, in processes for making sheets of photographic film such as 35 mm film, a long film web is fed along its longitudinal direction and cut sequentially into sheets of film having predetermined lengths, for example, 24-frame rolls of film or 36-frame rolls of film. The techniques for feeding a long web in its longitudinal direction in order to feed the long web to a fixed type cutter or to a moving type cutter, which cuts the web while it is moving at a speed equal to its feeding speed, and sequentially cutting the web with the cutter into sheets are widely used in various fields as well as in processes for making sheets of photographic film. One of such techniques has been disclosed in Japanese Unexamined Patent Publication No. 59(1984)-4548.
In cases where a fixed type cutter is used, the feeding of the web is stopped when the web is to be cut. In cases where a moving type cutter is used, though the speed at which the web is fed cannot be increased very much, it is required that the sheet which has been cut from the web be fed quickly into the subsequent process. Therefore, in both cases, the speed at which the sheet is fed changes midway during the feeding. As a result, the sheet slips along the feeding means such as feed rollers.
FIGS. 3A and 3B are schematic views showing an example of a conventional apparatus for feeding sheets wherein a fixed type cutter is used. The aforesaid problem will be described hereinbelow with reference to FIGS. 3A and 3B. A web 50, which is wound around a supply roller 51, is intermittently unwound and fed toward a cutter 53 by intermittent feed rollers 52, 52 until a leading portion of the web 50, which portion has a predetermined length, is located on the downstream side of the cutter 53 as viewed in the direction along which the web 50 is fed. This process occurs intermittently, each time the web 50 is to be fed forward. High speed feed rollers 54A, 54A, 54B, 54B, 54C, 54C which are rotated at equal speeds are provided on the downstream side of the cutter 53 as viewed in the direction along which the web 50 is fed.
As shown in FIG. 3A, immediately before the web 50 is cut, the unwound portion of the web 50 is held by the intermittent feed rollers 52, 52 and the high speed feed rollers 54A, 54A. At this time, the rotation of the intermittent feed rollers 52, 52 is stopped and the unwound portion of the web 50 is held in a stationary state, whereas the high speed feed rollers 54A, 54A continue to be rotated quickly. Therefore, the portion of the web 50 which is grasped by the high speed feeding rollers 54A, 54A slips along the high speed feed rollers 54A, 54A until the cutting of the web 50 is finished.
Also, as shown in FIG. 3B, a sheet 50A which has been cut from the web 50 is accelerated from a standstill to a predetermined feeding speed when the sheet 50A moves from the high speed feed rollers 54A, 54A to the high speed feed rollers 54B, 54B and then to the high speed feed rollers 54C, 54C. During the acceleration of the sheet 50A, the sheet 50A inevitably slips along the rollers because the high speed feed rollers 54A, 54A, 54B, 54B, 54C, 54C are being rotated at constant speeds.
When the sheet 50A slips along the rollers, it is often scratched by the rollers. In cases where the sheet 50A is photographic film or the like, scratches on the sheet 50A render the sheet 50A unmarketable.
One approach used to prevent the sheet 50A from being scratched is to decrease the nip pressures of the high speed feed rollers 54A, 54A, 54B, 54B, 54C, 54C. However, with this approach, the speed at which the sheet 50A is fed by the high speed feed rollers 54A, 54A, 54B, 54B, 54C, 54C fluctuates during the process for making the sheets. As a result, the time required for the sheet 50A to arrive at the position where the subsequent process is carried out fluctuates. In cases where the subsequent process is carried out with an automatic machine, fluctuations in the time required for the sheet 50A to arrive at the position where the subsequent process is carried out adversely affect the normal operation of the automatic machine. Particularly, in cases where a plurality of webs are fed in parallel and simultaneously cut into sheets and the resulting sheets are fed into the subsequent process in which a plurality of the sheets are simultaneously processed with an automatic machine, very serious problems arise when the time required for each sheet to arrive at the position where the subsequent process is carried out fluctuates.